The police and Pakistan's paramilitary forces have raided both Sunni and Shiite religious seminaries over the last two days, detaining an unspecified number of people, Sheikh said.

Sunni and Shiite activists have rallied in Karachi, protesting against the raids. One of the rallies by the Shiites blocked a highway for eight hours, which the police dispersed with tear gas. Police officer Razaq Khan said protesters clashed with police and pelted them with stones.

Pakistan's Sunni militants, many affiliated with the Taliban and al-Qaida, have long targeted minority Shiites, considering them to be heretics. The police suspect some of Karachi's recent sectarian killings of Sunnis could be the work of Shiite militants.

The raids also arrested two militants from the Taliban-linked sectarian group Lashkar-e-Jhangvi, who were allegedly involved in several killings, provincial chief minister Murad Ali Shah said. The police raids also sealed religious seminaries, he said, but he wouldn't say how many.

Pakistan has been fighting the Islamic militants and their sectarian allies for over a decade; the militants have a strong presence in urban areas and ties with Taliban and al-Qaida linked foreign militants in tribal regions along Afghan border.

Pakistan's military has launched several offensives in the tribal regions, which serve as safe havens for the militants.

Pakistani army chief on Monday confirmed the death sentences of nine Islamic militants after they were convicted by a military court. The militants were involved in the killings of army and police officers, a Pakistani army statement said.